Potatoes make you podgy… It’s proven!

The villain of the obesity epidemic is not cupcakes, fizzy drink or the Double Down. Sorry spud lovers, it is the humble potato, no matter which way you slice it.

A long-running Harvard University study has found that daily consumption of an extra serving of spuds – french fried, sliced into crispy chippies, mashed with butter and garlic, or simply boiled or baked – caused more weight gain than downing an extra can of sugary drink or eating an extra helping of red or processed meats.

After tracking the diet and lifestyle of more than 120,000 people from around the United States for at least 12 years, researchers calculated that participants gained about 360 grams a year. Their findings were published in the New England Journal of Medicine this week.

The United Nations declared 2008 the International Year of the Potato, praising it as a good source of vitamin C, several B vitamins and minerals, including iron, potassium, phosphorus and magnesium.

But when the Harvard team examined the potato’s role in the modern diet, they found that people who ate an extra serving of french fries every day gained an average of 1.5 kilograms over a four-year period. Those who munched on an extra serving of potato chips daily gained an average of 770g every four years, and an extra serving of potatoes prepared in any non-chip form was found to contribute to an average weight gain of 590g over four years.

Study co-author Walter Willett said that, because potatoes were always cooked before eating, it was easier for the body to transform the starch to glucose. Since spuds prompt a quick spike in blood sugar levels, they cause the pancreas to go into overdrive trying to bring levels back to normal. As blood sugar falls, people usually experience hunger, which leads to snacking.

Overall, the study found that quality of food is more important than quantity for preventing long-term weight gain, and that small lifestyle changes, such as more exercise and avoiding processed food, made the difference between staying slim and becoming overweight.